1. Field of the Invention
The present invention relates to an improvement in image stabilizing apparatus for preventing a blur of image of an optical equipment occurring for example due to hand vibration.
2. Related Background Art
Some optical equipments have been known to be provided with a function for preventing a blur of image caused for example by hand vibration.
For example, U.S. Pat. No. 2,959,088 and U.S. Pat. No. 2,829,557 and others disclose such apparatus in which a correcting optical system is arranged in a movable manner and its inertia is used to prevent a blur of an image.
FIG. 13 illustrates the overall construction of this type of image stabilizing apparatus, where lenses 1, 2 constitute an optical system for correcting an image blur for principal lenses 12, 13 which are fixed to a lens-barrel 4 (hereinafter referred to as "barrel") for forming an image on a focal plane 14. Supposing that f.sub.1 is the focal length of the lens 1 having a negative power and fixed to the barrel 4 and f.sub.2 is the focal length of the lens 2 having a positive power and supported on a movable support member 3, the focal lengths of the correcting optical system are determined to satisfy the following relationship: EQU f.sub.1 =-f.sub.2.
Said movable support member 3 is supported on the barrel 4 at the position spaced apart by the distance equal to the focal length f.sub.2 (=-f.sub.1) from the image side principal point of the lens 2 by means of gimbals 5 which are provided to effect a double-axle support.
FIG. 14 shows the construction of such double-axle support by the gimbals 5, where the movable support member 3 holding the lens 2 is supported by a support member 5y having a degree of freedom around the y-axis, while the support member 5y is supported by a support member 5x having a degree of freedom around the x-axis which is perpendicular to the direction of the y-axis, and furthermore the support member 5x is supported on the barrel 4 so as to construct an optical system having degrees of rotational freedom with respect to two axis.
Referring to FIG. 13, numeral 10 denotes a counter weight serving as a balancer to achieve a balance in the movable support member 3, mounted on the movable support member 3 at the side opposite from the lens 2 by interposing the gimbals 5 so that a balance with the lens 2 may be obtained with respect to the gimbal 5.
With the construction as described, it is possible to achieve a stabilizing optical system of the so-called inertia pendulum type. That is, by using a construction as shown in FIG. 13, a blur of image may be prevented in a manner which will be described below.
If for example the construction as shown in FIG. 13 is that of a telescope, an optical image of an object is formed on the focal plane 14 through the principal lenses 12, 13 and correcting optical system 1, 2 at the interior of the barrel 4 which is directed toward the object. In a telescope having a high magnifying power, if held by hand, a vibration having frequency components in the range of 0.1.about.10 Hz occurs at the barrel 4 such as due to a hand vibration and such vibration is responsible for a blur of image.
When the above described optical mechanism is used, however, the inertia of the movable support member 3 causes a relative displacement between the lens 2 and the lens 1 in response to such vibration, and the blur of image as described is to be restrained by the relative displacement between the lens 2 and the lens 1.
Referring to FIG. 13, a member 9 attached to the movable support member 3 is a conductor made of a nonmagnetic material such a piece of aluminum. A restraining force (damping force) corresponding to the vibrating rate of the barrel 4 is generated by the magnetic effect formed by magnets 6 and 7 which are fixed to the barrel 4. This is required to produce a damping effect so as to prevent the movable support member 3 from contacting the inner wall of the barrel 4 when the barrel 4 is abruptly displaced for example to change image composition.
In particular, a damping effect is obtained such that an eddy current occurring on the conductor 9 by the magnets 6, 7 as shown in the enlarged view in FIG. 15 generates a force in a direction so as to reduce the displacement of the movable support member 3 from the center of movement at which the optical axis of the lens 2 coincides with the optical axis of the principal lenses 12, 13 (principal optical axis 15).
It should be noted that, while the magnets 6, 7 in FIG. 15 are mounted only on the upper portion of the barrel 4 and thus an omission is made therein to facilitate the illustration, similar magnets are also provided at the lower portion as well as at the left and right of the barrel 4 so as to effect a double-axle support.
Referring to FIG. 13, numeral 11 denotes a magnetic body attached to the movable support member 3 integrally with the counter weight 10, effecting a centering operation by the magnetic effect produced in relation to a magnet 8 fixed to the barrel 4 to bring the movable support member 3 back to the center of the movable range at which the optical axis of the lens 2 coincides with the principal optical axis 15. Such centering operation is required to remove those portions of the displacement corresponding to a manufacturing error and the direct current component among the frequency components of the displacement so that the optical axis of the lens 2 coincides with the principal optical axis 15, because, if no vibration occurs, a better optical characteristic is obtained by using the center portion of the lens 2.
Specifically, the magnetic body 11 and the magnet 8 are placed to face each other by the same polarity (N-polarity) as shown in the enlarged view of FIG. 15, magnetically repelling each other. Since the center of the magnet 8 coincides with the principal optical axis 15, a centripetal force (centering force) is generated such that the optical axis of the lens 2 is caused to coincide with the principal optical axis 15.
Thus, the structure for damping and the structure for centering as described above can improve the characteristic of an image stabilizing apparatus which is based on the inertia pendulum method.
In actual taking, however, such operations as panning (in which the barrel 4 is horizontally moved to change the image composition) and tilting (in which the barrel 4 is vertically moved to change the image composition) are frequently performed to follow the subject or to change the subject.
The above described structures constitute a system for stabilizing operation fundamentally considering only a static condition where such operations are not to be performed. Although it produces a stabilizing effect for such vibrations as hand vibrations, an unnatural movement of image may result because for example the stabilizing effect is reduced or the correcting optical system remains at a position largely deviated in one direction or collides with the inner wall of the barrel 4 due to the movement in practical panning or tilting where a unidirectional movement is to be continued.
Thus, the present applicant has filed an application (U.S. patent application Ser. No. 516,303) in which control functions for giving torques around the x-axis and y-axis are set in the image stabilizing system to adjust the operation with respect to panning and tilting so that control of the correcting optical system is achieved in accordance with such control functions. Such apparatus mainly includes: a torque generation means for controlling the movement of the correcting optical system to prevent a collision with the inner wall of the barrel which tends to occur such as in panning and tilting operations; a control signal generating means for controlling said generation means; and a position detecting means for detecting the state of displacement of the correcting optical system in relation to the barrel as an input signal for processing to generate the control signal.
The control signal generating means as described gives a non-linear torque in response to the displacement of the movable support member 3 which constitute an inertia pendulum so as to satisfy two opposing factors that are the prevention of an excessive movement and stabilization of the lenses related to panning or tilting.
An example of the characteristic of such control torque is shown in FIG. 16.
With the characteristic of the control torque as shown in FIG. 16, a torque for centering and damping is hardly generated when the movable support member 3 is positioned near the center of movement so as not to impede the stabilizing effect by the inertia pendulum. When for example the barrel 4 is moved in a considerable degree toward one direction such as for panning, however, if the movable support member 3 is largely displaced from the center of the movement due to the effect of the inertia pendulum, centering and damping force increasing sharply with a further increase in such displacement is generated to bring the movable support member 3 back to the center of movement, i.e., to produce a large control torque. Thus it is possible to prevent the collision of the movable support member 3 with the inner wall of the barrel 4.
Since however there is a limit in the amount of signals to be read from the position detecting means by the above described control signal generating means, the resolution is necessarily lowered for example in the above described correcting optical system where the movable range is wide, resulting in a problem that the above described torque control cannot be accurately performed.
Further, while to some extent an inaccuracy in the control torque is not much of a problem if the correcting optical system is largely displaced from the center of movement as it is the state where a large deviation is occurring, there has been a considerable problem that an inferior resolution causes an excessive movement of the correcting optical system due to the centering force and dampling force as described when the correcting optical system is near the center of movement as it is the state where the deviation is not too large, and as a result not only the stabilizing effect is impeded but also the correcting optical system is caused to vibrate (reciprocate).